In a Frequency Division Duplex (FDD) system, quantization of Channel State Information (CSI) is a key issue. A Uniform Circular Array (UCA) is a typical antenna configuration of a base station. One way to quantize Channel State Information for UCA is to reuse a Rel-10 codebook. However the 8Tx Rel-10 codebook is designed for a linear antenna array but not well suitable for a uniform circular array.
A full codebook suitable for antennas configured in a uniform circular array has been absent so far.